Golf club manufacturers have proposed various golf club heads with enhanced shape restitution so that amateur golfers are capable of driving a golf ball over a long distance. In recent years in particular, this has been achieved through improvements in golfclub head structures and materials.
Another method which has been used since earlier times for improving the striking distance of a golf ball consists of forming a cavity inside the club head and partly filling the cavity with a movable mass such as one or more metal slugs, metal beads or liquid mercury. Upon contact of the golf club with a golf ball during a strike, the club head decelerates to some extent and the movable mass therein strikes the forward end of the cavity, thereby transmitting a backlash impulse to the face of the club head.
Prior inventors have obtained longer and straighter shots using golf clubs having these backlash impulse devices mounted therein. In that regard, the following documents constitute a good inventory of backlash impulse devices of the prior art for golf clubs and other sport implements.
The first series of documents describe various golf club heads each having a cavity therein partly filled with mercury. As the club head strikes a ball, the liquid mercury dashes against the forward end of the cavity and transmits its inertia to the club face, for increasing the energy transmitted to the ball. This general concept has been disclosed in the following documents;    U.S. Pat. No. 1,561,595 issued to T. J. Davis on Nov. 17, 1925;    U.S. Pat. No. 2,067,556 issued to W. L. Wettlaufer on Jan. 12, 1937;    U.S. Pat. No. 3,951,413 issued to B. Bilyeu on Apr. 20, 1976;    U.S. Pat. No. 3,993,314 issued to L. E. Harrington et al., on Nov. 23, 1976;    U.S. Pat. No. 4,655,458 issued to R, I. Lewandowski on Apr. 7, 1987;    U.S. Pat. No. 5,628,697 issued to C. L. Gamble on May 13, 1997;    U.S. Pat. No. 5,890,973 issued to C. L. Gamble on Apr. 6, 1999;    U.S. Pat. No. 6,641,490 issued to J. W. Ellemor on Nov. 4, 2003;    U.S. Pat. No. 6,551,199 issued to A. A. Viera on Apr. 22, 2003;    CA Patent 386,137 issued to W. L. Wettlaufer on Jan. 9, 1940.
The second series of documents listed herein below describe club heads each having one or more cavities therein and one or more metal slugs or metal pellets mounted inside these cavities. The loose pieces are movable inside the club head to strike the back side of the striking surface when the club strikes a ball. These documents are;    U.S. Pat. No. 0,690,940 issued to H. B. Febiger on Jan. 14, 1902;    U.S. Pat. No. 1,825,244 issued to J. J. Nero on Sep. 29, 1931;    U.S. Pat. No. 2,592,013 issued to T. F. Curley on Apr. 8, 1952;    U.S. Pat. No. 3,589,731 issued to C. W. Chancellor, Jr., on Jun. 29, 1971;    U.S. Pat. No. 5,046,740 issued to R. A. D'Eath on Sep. 10, 1991;    U.S. Pat. No. 5,121,922 issued to R. L. Harsh, Sr., on Jun. 16, 1992;    U.S. Pat. No. 5,613,916 issued to R. Sommer on Mar. 25, 1997;    U.S. Pat. No. 5,776,009 issued to J. P. McAtee on Jul. 7, 1998;    U.S. Pat. No. 5,803,829 issued to T. Hayashi on Sep. 8, 1998;    U.S. Pat. No. 7,037,213 issued to M. Otoguro on May 2, 2006.
The concept of using a movable mass to generate a backlash impulse has also been used in other sport implements, and for example in tennis rackets, as described in the following documents;    U.S. Pat. No. 4,057,250 issued to W. G. Kuban on Nov. 8, 1977;    U.S. Pat. No. 4,353,551 issued to S. Arieh et al., on Oct. 12, 1982.
Other inventors have recognized the fact that the energy transmitted to a ball by a striking implement is depending upon a relationship between the natural restitution of the ball surface and the natural restitution of the striking surface of the sport implement. The following document describes a method to match the natural frequency of a golf club with the natural frequency of a golf ball, so that the restitution of their respective surfaces are in phase with each other. This document is;    U.S. Pat. No. 4,928,965 issued to T. Yamaguchi et al., on May 29, 1990;
The same concept has also been applied to a baseball bat as described in;    U.S. Pat. No. 5,816,963 issued to R. Brooks et al., on Oct. 6, 1998.
Although the prior art on the subject of backlash impulse devices is extensive, it is believed that an important aspect of the dynamics involved in this science has been overlooked in the past. It is believed that a timing of a backlash impulse in relation with the time of contact between a ball and the striking surface of a club head is very important, and has not been addressed in prior art literature.
It will be appreciated that if a backlash impulse occurs when the striking surface of a club has not yet reached its elastic limit during a strike, this impulse has a detrimental effect of lessening the elastic deflection of the striking surface, and thereby lessening the amount of energy transferred to the ball. On the other hand, if the impulse occurs after the ball has left the striking surface, it has no effect at all on the striking distance.
Contrary to accepted wisdom in the art, it is believed that backlash impulse devices cannot be readily mounted into golf clubs available for sale, and be used by any golfer irregardless of their swing speeds. It is believed that the time period available for obtaining advantageous results with such a device is a narrow time range within the first vibration cycle in the club face following an impact. It is believed that the backlash impulse must be synchronized to occur within this narrow time range.
Therefore, it is believe that a need exists in the golf club manufacturing industry for a method to calibrate the timing of a backlash impulse with both the swing speed of a golfer and the natural frequency of the striking surface of the club used by that golfer, so that the impulse has a maximum effect on a struck ball.